Yes,you can do this on-line.
See this link for detail on how to do this: https://www.colorado.gov/pacific/tax/e-filer-attachments-instructions-and-forms
"How to Submit an E-Filer Attachment in Revenue Online
E-Filer Attachments (what had previously been done exclusively with the DR 1778 E-Filer Attachment paper form), may be uploaded into Revenue Online without logging into a taxpayer’s income tax account.
- Go to Revenue Online. "
"When Colorado income tax returns are filed electronically through Federal/State Electronic Filing (FSEF) or through Revenue Online, supporting documentation must be submitted to prove eligibility for credits claimed. Scanning. saving and uploading an electronic copy of the documentation through Revenue Online is the preferred method of submitting these documents because the copy will be in the taxpayer’s account and the department will not need to ask for an additional copy later. The alternative method is to send the documentation by mail with the form DR 1778 "E-Filer Attachment Form." The DR 1778 serves as a kind of "cover letter" for the documents when they arrive at the department by mail."
